A 60-year-old man shows a predominance of kappa light chains in lymphocytes. What does this suggest?

The predominance of kappa light chains in lymphocytes suggests a clonal lymphoid proliferation, which is indicative of a monoclonal gammopathy. In normal physiology, B cells produce both kappa and lambda light chains, with their ratio generally being about 3:1 in favor of kappa chains. However, when there is an overrepresentation of one type of light chain, such as kappa, it implies that a specific clone of B cells is proliferating more than others. This is often seen in neoplastic conditions like multiple myeloma or other lymphoproliferative disorders.

The presence of a predominance of kappa light chains points towards a pathological process where a single clone is expanding, leading to the manifestation of symptoms associated with that proliferation. This finding is significant in the diagnostic workup for conditions like multiple myeloma, where monitoring of light chain production can help assess the disease and its response to treatment.